1. Field of the Invention
This invention relates to a novel catalyst which is useful for the hydrotreatment of heavy hydrocarbon oils, and a method of preparing such a catalyst. This invention is also concerned with a process for hydrotreating heavy hydrocarbon oils.
2. Description of the Prior Art
Heavy hydrocarbon oils such as heavy crude oils, reduced crude oils, vacuum residues, heavy oils extracted from tar sand and mixtures thereof, contain non-distillable, high molecular coke precursors usually called asphaltenes which are insoluble in light hydrocarbons such as pentane and heptane, and undesirable impurities such as oil-soluble organic metal compounds containing vanadium, nickel or the like and sulfur or nitrogen compounds. These impurities are often found for the greater part in high molecular hydrocarbon fractions, such as asphaltenes. This is a significant cause for the difficulty involved in the catalytic hydrotreatment of heavy hydrocarbon oils. The term "hydrotreatment" used herein means the treatment of heavy hydrocarbon oils in a hydrogen atmosphere for the purpose of converting asphaltenes and other high molecular hydrocarbon fractions in the heavy hydrocarbon oil into distillable hydrocarbon fractions, or hydrocarbon fractions which are soluble in a light hydrocarbon, to thereby reduce any such high molecular fraction, and simultaneously removing or reducing the aforementioned metal, sulfur and nitrogen compounds.
Hydrodesulfurization and hydrocracking are known to be effective processes for obtaining high grade light oils from heavy hydrocarbon oils on a commercial scale. These processes employ a fixed or ebullated bed of a catalyst composed of a metal such as cobalt, nickel, molybdenum and tungsten supported on a carrier formed of activated alumina such as .gamma.-alumina, .eta.-alumina and .chi.-alumina, or silica alumina, or the like. [M. W. Ranney, Chemical Technology Review No. 54, Desulfurization of Petroleum, Noyes Data Corporation, New Jersey (1975).] These processes, however, encounter a number of problems if the heavy hydrocarbon oil to be treated contains asphaltenes and heavy metals. The asphaltenes in the oil are in the form of colloidally dispersed macromolecules, and cannot easily diffuse into the active sites in the pores of the catalyst. This seriously inhibits the hydrocracking of the asphaltenes. The presence of asphaltenes heavily promotes the formation of coke and carbonaceous matters, which leads to a considerable reduction in the activity of the catalyst. These problems define a great obstacle to the industrial-scale hydrotreatment of heavy hydrocarbon oils.
A further problem, which is as important as those hereinabove discussed, is due to the presence of a large amount of heavy metals in the oil. These metals can deposit on the catalyst surface during hydrotreatment, thereby to poison the catalyst and shorten its life sharply.
The catalytic hydrotreatment of heavy hydrocarbon oils by the known processes requires frequent renewal of the catalyst, and a heavy consumption of the catalyst relative to the oil to be treated. In the event the known process is selectively intended for decomposing asphaltenes to produce light oil, it is necessary to enhance the activity of the catalyst. This necessarily requires stringently selected conditions for the reaction so that the degradation of the catalyst is further promoted and the light oil produced undergoes cracking and gasification. This disables a high-yield production of light oil, and brings about a seriously uneconomical increase in the consumption of hydrogen.
Members of the group to which the inventors of this invention belong have been engaged in extensive research for several years with a view to finding out a catalyst which overcomes the aforementioned disadvantages of the known catalyst and which is effective for the catalytic hydrotreatment of heavy hydrocarbon oils. As a result, they have discovered that a sepiolite catalyst is particularly effective for the hydrotreatment of hydrocarbons, particularly for the removal of heavy metals therefrom. They have already obtained patent protection for a process for removing metals from hydrocarbons by using such a catalyst, and a process for preparing the catalyst (U.S. Pat. Nos. 4,152,250 and 4,196,102).
They have also discovered that clay minerals of the double-chain structure, including sepiolite, have a pore structure which is effective for the hydrotreatment of heavy hydrocarbon oils, and that a specific type of vanadium sulfide is active for the hydrotreatment of heavy hydrocarbon oils, particularly for the decomposition of asphaltenes and the removal of heavy metals therefrom. Based on this discovery, they have applied for a patent on a catalyst compound of such a clay mineral and vanadium sulfide for the hydrotreatment of heavy hydrocarbon oils, and a process for preparing such a catalyst (U.S. Ser. No. 84,764).
There have been many proposals which suggest addition of a second component into a solid oxide catalyst as a filler, diluent, dispersant, molding assistant or reinforcing agent, or the like (U.S. Pat. No. 3,118,845, British Pat. No. 1,218,080, Japanese Patent Publication No. 31878/1974, Japanese Laid-Open Patent Application Nos. 36595/1974, 40494/1975, 142492/1975 and 82690/1977, etc.). The aforementioned U.S. Pat. Nos. 4,152,250 and 4,196,102 also teach that it is effective to add an ordinary alumina sol as a molding assistant.